(1) Field of the Invention
The invention deals with fabrication of biodegradable green cellulose ester nanocomposites from a plasticized cellulose ester bioplastic and various organically modified clays in presence of a novel compatibilizer, such as maleated cellulose ester.
(2) Description of Related Art
Green nanocomposites are the wave of the future and are considered as the next generation of new materials. The lofty goals set by U.S. governments for the creation of bio-based economy present significant challenges to Industry, Academia and Agriculture/Forestry. Cellulose from trees is attracting interest as a substitute for petroleum feedstock in making plastic in the commercial market. Different raw materials such as cotton, recycled paper, wood cellulose, and sugarcane are being used in making cellulose ester biopolymers. Cellulose esters (such as Cellulose acetate or CA, Cellulose acetate propionate or CAP, and cellulose acetate butyrate or CAB) are considered as potentially useful biodegradable polymers of the future.
U.S. Pat. No. 3,922,239 describes a mixture of cellulose esters or ethers which are mixed with polymeric cyclic esters, such as oligomer of .epsilon.-caprolactone. This substance is said to be thermoplastic. It was found that the components of the mixture do not posses satisfactory compatibility. This is shown by the fact that during the thermoplastic processing no homogeneous melt is obtained. To some extent even a de-mixing can be observed during the processing.
GR-A-2 152 944 describes plasticized cellulose acetates which were obtained from the reaction of cellulose acetate having a free hydroxyl group with a cyclic ester, in particular ε-caprolactone, in the presence of a catalyst. The weight ratio of the cellulose acetate to the cyclic ester is said to be between 1/99 and 95/5 and the polymerization temperatures are said to be between 120° and 230° C. The quantity of cyclic ester which is to be reacted with the hydroxyl group-containing cellulose acetate, is preferably between 0.5 and 4.0 mol units per anhydroglucose unit of the cellulose acetate. The melting temperature of the plasticized cellulose acetate is reduced through an “inner” plasticization. The decomposition temperature is simultaneously raised.
U.S. Pat. No. 4,529,788 deals with a process for the production of graft polymerization in which a cyclic ester is subjected to a catalyzed ring-splitting polymerization in the presence of a cellulose derivative.
Polymer-nanocomposites research is primarily concerned with commercial nonbiodegradable thermoplastics like nylon, polypropylene (PP), thermoplastic polyolefin (TPO) and thermosets like epoxies, polyesters, and the like. Biodegradable nanocomposites from starch plastic and clay are known in the literature and such efforts are targeted for packaging applications.
It is also well known in the prior art to heat fillers of the nanocomposite type to provide the polymer matrix to improve the interfacial adhesion of the mineral to the matrix. For example, in Papalos, U.S. Pat. No. 3,227,675, kaolin clays are described, the surfaces of which are modified with organofunctional silanes. Additional references of this type include Iannicelli, U.S. Pat. Nos. 3,290,165 and 3,567,680. Similarly, in U.S. Pat. No. 4,789,403 to Rice and U.S. Pat. No. 6,828,367 to Campbell, a method is disclosed for producing a layered lattice silicate which is surface modified with an organic material. The layered lattice silicate is contacted with an organic monomer, comonomers, or a pre-polymer, and surface polymerization or reaction in situ is affected in the presence of a gaseous hydrogen atmosphere. Among the organic monomers that can be used in the process are various precursors of nylon.
Recently, disclosures in producing composite materials composed of a polymer and a smectite-type clay mineral, with the mineral being connected to the polymer through ionic bonding. For example, in Kawasumi et al., U.S. Pat. No. 4,810,734 a process is disclosed wherein a smectite-type clay mineral is contacted with a swelling agent in the presence of a dispersion medium thereby forming a complex. The patent states that the swelling agent acts to expand the interlayer distance of the clay mineral, thereby permitting the clay mineral to take monomers into the interlayer space. The swelling agent is a compound having an onium ion and a functional ion capable of reacting and bonding with a polymer compound. Examples of polymers used in this system are polyamide resins, vinyl polymers, thermosetting resins, polyester resins, polyamide resins and the like. Related disclosures are found in U.S. Pat. No. 4,739,007 to Okada et al and U.S. Pat. No. 4,889,885 to Usuki et al.
U.S. Pat. No. 5,480,922 to Mulhaupt et al; U.S. Pat. No. 3,922,239 to Koleske et al., U.S. Pat. No. 4,529,788 to Asami et al, U.S. Pat. No. 5,554,670 to Giaannelis et al.
There are three common processes for fabricating polymer-clay nanocomposites. They are melt compounding; solution processing; and in-situ intercalation polymerization. In the usual melt compounding technique the polymer pellets and clay are extruded to derive the polymer-clay nanocomposites. For uniform mixing of clay and polymer granules; both the clay and the polymer are sometimes extruded twice. The extruded samples are further injection molded or compression molded to provide the test specimens.
Phthalate plasticizers, used in commercial cellulose acetate plastic, pose an environmental and perhaps a health threat and thus it is a serious concern about their long-term use. Plasticized CA is a potentially useful biodegradable polymer of the future with considerable toughness, excellent optical clarity. It has, however, low dimensional stability under high humidity and elevated temperature, and high melt processing temperature. Therefore, the flow properties are low for automotive and packaging applications. Improvement of flow properties of CA or CAB can be done through plasticization using plasticizer like phthalates or glycerol. Unfortunately, the existence plasticizer migration greatly decreased mechanical properties.